The present invention relates to a network apparatus that forms a server-client system, and particularly to an apparatus and a method for controlling the band of communication (volume of traffic) from a server to a client, the apparatus being placed between a server farm comprising a single server or a plurality of servers and a LAN that bundles client apparatus.
In IEEE802.3, there are specifications provided for the local area network (LAN). Many network systems are formed by the LAN specified in IEEE802.3.
In recent years, the apparatus that forms such a network system has changed in its main element from the hub apparatus used to construct a shared bus network to the LAN switch used to construct a switching network. As the network apparatus has changed, links which connect the network interfaces of the apparatus forming a network system have also changed. More specifically, half duplex links used in the conventional shared bus have been replaced with full duplex links. The full duplex link allows the apparatus connected to the link to transmit and receive data to and from each other simultaneously. The apparatus that forms a network system is, for example, a network apparatus such as a LAN switch, a host apparatus such as a server/PC, or the like.
The full duplex link is provided with different communication lines each for transmission and for reception. In the full duplex link, collision between transmission data and reception data is not caused, and therefore the apparatus on the transmitting side is able to transmit frames continuously. However, if the transmission traffic of the frames exceeds the capacity of the apparatus on the receiving side to process received data, the apparatus on the receiving side abandons frames. As a means to avoid the abandoning of frames, there are provided specifications called IEEE802.3x. IEEE802.3x relates to a technology that temporarily stops the transmission traffic between the apparatus connected to each other by a full duplex link.
IEEE802.3x specifies a case where of the two apparatuses connected to each other by a full duplex link, one apparatus needs to stop frame transmission from the other apparatus for a certain period of time. In this case, the apparatus on the receiving side transmits a control frame called “PAUSE” to the other apparatus. After receiving the PAUSE frame, the other apparatus will stop frame transmission for a period of time specified by the PAUSE frame.
Specific details regarding the PAUSE frame will be explained with reference to FIG. 15.
As shown in FIG. 15, a network apparatus 151 and a server apparatus 3 connected to each other by a full duplex link 2 are provided with MAC (Media Access Control) chip sets 4 and 5, and MAC control units 6 and 7, respectively. If the MAC chip sets 4 and 5 and the MAC control units 6 and 7 are provided with the PAUSE function specified in IEEE802.3x, they operate as follows.
The MAC control units 6 and 7 receive instructions for the transmission of a PAUSE frame including information on PAUSE time from host programs or the like. The MAC chip sets 4 and 5 create a PAUSE frame in which the specified PAUSE time is set, according to the transmission instructions. The MAC chip sets 4 and 5 transmit the PAUSE frame after it is created. In addition, the MAC chip sets 4 and 5 receives a PAUSE frame from the apparatus to which the MAC chip sets 4 and 5 are connected through the link 2. The MAC control units 6 and 7 decodes the content of the received PAUSE frame. After decoding the content of the received PAUSE frame, the MAC control units 6 and 7 set the specified PAUSE time in built-in PAUSE timers 8 and 9. After setting the PAUSE time, the MAC control units 6 and 7 wait until the frame transmission being performed at the time when the PAUSE time was set is completed. The MAC control units 6 and 7 starts the PAUSE timers 8 and 9 after the frame transmission is completed. As a result, frame transmission is suspended for a period of time until the PAUSE time passes.
The PAUSE time is specified in a range of 1 to 65535. The unit of one PAUSE time period represents the time required for the transmission of one 64-byte frame. This represents the time spent in the transmission of 512 bits (512-bit time).
In the meantime, the configuration of the intranet has changed in recent years. As the configuration of the intranet has changed, the rate of communication traffic between an enterprise server group (server farm) at the center of the organization and clients at each division has increased. In addition, there have appeared the high-speed LAN as specified in IEEE802.3z as well as the link aggregation technology (specified in IEEE802.3ad), a high-speed connection system between apparatus. The advent of such a system and technology has created a tendency for transmission traffic from the server apparatus to be increased. Incidentally, traffic means communication band volume, and transmission traffic means transmission band volume per unit of time.
Generally, in a server-client system, the band of a LAN where end clients are connected is small. Therefore, if transmission traffic from the server apparatus is heavy, congestion occurs at an intermediate network apparatus. The network apparatus abandons frames as congestion occurs.